1. Field of the Invention
The present invention relates generally to infrared-light sensors and more specifically to a heat-sensitive infrared-light image sensor formed by an array of infrared-light sensitive cells where the individual output levels of the cells tend to vary with temperature. The present invention is concerned with an apparatus and method for compensating for the temperature-dependent drift components of the individual cells of the image sensor.
2. Description of the Related Art
Infrared-light image sensors of the heat-sensitive type comprise a matrix array of infrared-light cells each being formed by a switching transistor and a thermoelectrical conversion element fabricated in a bolometer structure using titanium. The cells are scanned to produce a video signal as a sequence of video samples. Because of the inherent thermal sensitivity, the intensity of each video sample varies with the temperature of the device and this temperature increases with time in such a manner that a device temperature variation of 1.degree. C., for example, corresponds to a 500.degree. C. temperature variation on the surface of a radiant object. In addition, there exists sensitivity variability due to varying thermal coefficients and varying resistance values from cell to cell. Such variability is known as fixed pattern noise (FPN) and can be easily canceled by DC-level offsets obtained from the image sensor when it is maintained at a predetermined low temperature and shielded from radiation. However, due to the temperature-related variation of the heat-sensitive image sensor, the DC-level offset values are not valid for canceling the variability when the image sensor is in actual use.